For a pithy insight into depression, I like "I Had a Black Dog" and "Living with the Black Dog" by Matthew Johnstone.

http://www.amazon.com/Had-Black-Dog-...7898983&sr=8-1
http://www.amazon.com/Living-Black-D...7899022&sr=1-2

They are a series of cartoons with captions which, for me, ring so many bells and it's not too much for anyone who is trying to understand depression.